This application claims priority of French Application No. 9706891, which was filed on Jun. 4, 1997, and PCT Application No. PCT/EP98/03434, which was filed on May 28, 1998.
1. Field of the Invention
The invention relates to an electronic plug-in unit which includes an improved heat-dissipation device.
2. Description of the Prior Art
There are many uses of electronic plug-in units. One application consists, for example, in using them to produce radiotelephone links in a rural environment within the context of mobile telephony. This type of link thus makes it possible to avoid the costly laying of cables in order to link two points which are isolated and/or difficult to access.
Such electronic plug-in units make it possible to produce between two and sixteen 2-megabit telephone links. of course, the application mentioned is merely one example, electronic plug-in units being in fact intended for many uses which depend, in particular, on the nature of the electronic cards which they contain.
An electronic plug-in unit generally comprises several specific electronic cards which are linked via connection pins, on the one hand, to related electronic modules and, on the other hand, to external electronic modules which themselves are linked to an external antenna so as to be able to transmit and/or receive information via radio waves, for example. Each card supports components such as integrated circuits, for example, which have the drawback of generating heat. To allow proper operation of the electronic cards contained in the plug-in unit, it is therefore necessary to dissipate this heat generated by the heating components and to remove it to the outside.
A known solution consists in placing a fan inside the electronic plug-in unit. However, this solution cannot be envisaged as the presence of a fan involves very frequent maintenance operations, especially for cleaning or changing the fan""s filters. In point of fact, the electronic plug-in units are intended to be distributed in large numbers and to be installed in isolated places access to which is sometimes difficult. It is therefore impossible to envisage carrying out very frequent maintenance operations. Moreover, the addition of such a fan results in a significant reduction in the MTBF (mean time before failure) of the plug-in unit which, for example, drops from 8 years to 2 years, approximately. This solution is therefore inconceivable.
Currently, the heating components are thermally coupled to commercial heat sinks. These heat sinks are therefore preferably placed either on the edges of the electronic cards or on a side edge of the plug-in unit into which the electronic cards are inserted. Consequently, the heat dissipation is improved. Moreover, the electronic cards must be placed in the plug-in unit, along slides, in such a way that these cards are sufficiently far apart for natural convection to be able to occur. The distance between the cards may be about 10 centimeters. In addition, the plug-in unit is necessarily aerated, by means of small apertures made in its walls, so as to allow the heat to be removed to the outside by natural ventilation.
Moreover, when several electronic plug-in units are placed in an integrating rack, they must necessarily be spaced sufficiently far apart to allow the internal heat to be removed through their apertures by convection and natural ventilation. This distance between the plug-in units is typically between 20 and 40 centimeters, approximately.
Current plug-in units are therefore very bulky since they have a thickness which is generally greater than 8 cm, and they result in a waste of space in the integrating racks since they cannot be stacked one on top of another.
Furthermore, the constraint of placing the heating components along the edges is sometimes not readily compatible with the architecture of an electronic card to be produced.
The present invention solves the aforementioned problems by providing a thin electronic plug-in unit which includes a central core capable of draining away, by thermal conduction, the heat generated by the heating components located on the electronic cards.
The electronic plug-in unit includes a solid central core made of metal lying parallel to the plane of the plug-in unit in a position intermediate between two layers of electronic cards, so as to drain away heat, by thermal conduction, to at least one lateral radiator forming one of the said lateral edges of the plug-in unit. It is very compact with a small thickness, typically less than 10 cm. The central core, forming a heat sink, makes it possible not only to improve the heat dissipation of the plug-in unit, by the effect of thermal conduction to the lateral radiators, but also to ensure good mechanical integrity of the plug-in unit since the electronic cards and the top and bottom covers, intended to close off the plug-in unit, are directly fixed to this heat sink. In addition, the top and bottom covers of the plug-in unit do not necessarily have apertures since the heat is dissipated laterally to the outside by thermal conduction, and not by convection, which is associated with natural ventilation. When they do not have apertures, the covers of the plugin unit allow it to be hermetically protected from external attack. Furthermore, since the heat is no longer removed to the outside by natural ventilation, several plug-in units can be stacked one on top of another in an integrating rack, which saves space.